7

I am always confused about how to calculate safety altitude, especially when it comes to even heights and odd heights, e.g. is 7500ft even or odd?

SentryRaven
  • 15,660
  • 64
  • 88
user8165
  • 91
  • 1
  • 2
  • 3

7 Answers7

11

See below for the wording of 14CFR91.159 which is the reg you need to answer this question. Note it says "Odd [or Even] thousand feet plus 500". 7000 is an odd thousand even though it is an even number.

§ 91.159 - VFR cruising altitude or flight level.

Except while holding in a holding pattern of 2 minutes or less, or while turning, each person operating an aircraft under VFR in level cruising flight more than 3,000 feet above the surface shall maintain the appropriate altitude or flight level prescribed below, unless otherwise authorized by >ATC:

(a) When operating below 18,000 feet MSL and—

(1) On a magnetic course of zero degrees through 179 degrees, any odd thousand foot MSL altitude 500 feet (such as 3,500, 5,500, or 7,500); or

(2) On a magnetic course of 180 degrees through 359 degrees, any even thousand foot MSL altitude 500 feet (such as 4,500, 6,500, or 8,500).

Community
  • 1
Skip Miller
  • 10,312
  • 28
  • 53
10

Look at the thousands of feet only.
Is 7(thousand) even or odd?

I'm sure a mathematician views 7,500 as equally close to 8,000 as 7,000.

But in aviation terms, it is 7,000 plus another 500 feet, and therefore an odd altitude.

abelenky
  • 30,696
  • 9
  • 92
  • 143
3

In the US there is a simple rhyme memory trick that you can use to figure out what altitudes would be valid for you to fly both VFR and IFR.

EAST IS LEAST - WEST IS BEST

What that means is that you fly odd number altitudes when flying East (Magnetic) and even number altitudes when flying in a magnetic Westbound direction. For VFR just add 500 ft.

So valid West bound flights would be: 4000,6000,8000 IFR : 4500,6500,6500 VFR

Same with East Bound: 5000,7000,9000 IFR : 5500,7500,9500 VFR

A simple rhyme that works pretty well for me. Also BTW, if you are filing then chose the initial leg as your filing altitude. If you are under ATC control, you'll see that ATC will eventually ask you to climb or descend if your course leg changes your direction. IF VFR, and you make a bend that takes you to the other side, then climb or descend even if you are not talking to ATC. If talking to ATC, let them know. They can either tell you to stay put or pilots discretion to the new altitude.

The reason for this is that head on's are pretty hard to do if everyone is flying the same direction. You might get chewed up in the tail, but that's the job of the pilot in the plane overtaking you or ATC.

TB Flyer
  • 209
  • 1
  • 5
  • 1
    Welcome to the Aviation Stack Exchange! The rhyme you mention is great for converting true to magnetic headings, but why does "least" mean "odd"? – NathanG Apr 19 '15 at 21:16
  • I remember it from my first flying days about 28 years ago when my flight instructor explained both magnetic correction and well as flying directions. He said there were many mnemonics to remember but remember that it also applies to correcting magnetic headings +/- as well then you would only have to remember one of them. As a beginning student pilot he knew that too much information could overload a newbie and get you confused. – TB Flyer Apr 19 '15 at 21:36
  • 1
    “Least” is 5 letters, so it’s odd. “Best” is 4 letters, so it’s even. – Kolom Feb 02 '20 at 21:38
  • @Kolom comment: Finally! I've started to think I'm the only one poor soul studying IFR rules and consistently confusing when to use odd and when even. No CFI (CRI) around me was kind enough to spell any useful mnemonic or at least any useful reasoning (even some foolish/childish/obscene one) helping to recall the rule correctly each time after couple of weeks of yet another futile attempt of memorizing it. I've never had such challenge even during my fights with PPL exams but this rule somehow got outstanding in its complete and illogical inexplicability. – Van Jone Mar 29 '23 at 23:41
  • @VanJone Yeah this is frustrating at times, but after you ingrained it in your brain, you just forget how stupid it is when you first hear it. And you become a proponent. It's even funnier how we do it in my native language; the word "east" starts with D, and the word "west" starts with B. D has one hole, B has two holes, and that's your odd and even. :) – Kolom Mar 30 '23 at 05:49
3

I don't find any of the other answers to provide a useful mnemonic, which is what you need for rote memorization of arbitrary rules like this. The one I learned (and still remember decades later) is this:

ONE = Odd for North and East

In other words, if you're on a North or East course (360 - 179), then use Odd thousands.

By elimination, if you're on a South or West course (180 - 359), then use Even thousands.

StephenS
  • 27,747
  • 3
  • 62
  • 109
2

I just remember that East is Odd, because East is Even woud make too much sense.

Like Nav lights - Red on the the left, because Red on the Right would make too much sense.

CrossRoads
  • 8,795
  • 1
  • 19
  • 32
2

NEodd, SWeven, North to East “odd” altitude plus 500. SWeven, South to West “even” altitude plus 500. East is least and West is best is for magnetic variation when figuring true course ves magnetic course.

Mac
  • 21
  • 1
  • 2
    Hi and welcome to ASE, what country/countries does this apply to? And what about sectors E-S and W-N? – Jpe61 Feb 02 '20 at 20:17
  • 1
    Your answer is very jumbled... – Michael Hall Feb 03 '20 at 05:49
  • AFAIK, different countries aligned along N-S axis use different odd / even assignments, it seems your examples relate to New Zealand, don't they? E-W seems to be way more consistent assignment but finding a good mnemonic on it was rather challenging. – Van Jone Mar 29 '23 at 23:48
1

“East is Odd, West is Even Odder” is a pilots mnemonic to remember what altitudes to fly at under visual and instrument flight rules. First, east and west are defined by the magnetic headings of zero to 179 degrees (East) and 180-359 degrees (West.)

Paul Hanna
  • 11
  • 1